A model for force transmission through the cytoskeleton (CSK) is presented. I first discuss the physical principles that underlie this phenomenon and argue that mediation of focused forces is essential for control over mechanical signals. The difficulties of conventional continuous models in describing such mediation are traced to a fundamental assumption rather than to their being continuous. Relevant advantages and disadvantages of continuous and discrete modelling are discussed. It is concluded that favouring discrete models is based on two misconceptions, which are clarified. The model discussed here is based on the idea that focused propagation of mechanical stimuli over large distances can only occur when considerable regions of the CSK are isostatic. The concept of isostaticity is then explained and a recently developed continuous isostaticity theory is briefly reviewed.
The model enjoys several advantages: it leads to good control over force mediation; it explains nonuniform stresses and action at a distance; it is continuous, making it possible to model force propagation over long distances; and it enables prediction of individual force paths. To be isostatic, or nearly so, CSK networks must possess specific structural characteristics, and these are quantified. Finally, several experimental observations are interpreted using the new model and implications are discussed. It is also suggested that this approach may give insight into the dynamics of re-organisation of the CSK . Many of the results are amenable to experimental measurements, providing a testing ground for the proposed picture, and generic experiments are suggested.